This invention relates to inks employed in ink-jet printing, and, more particularly, to an ink composition especially suitable for thermal ink-jet printers.
In thermal ink-jet printing, resistive heating is used to vaporize the ink, which is expelled through an orifice in the ink-jet pen toward the paper substrate. Such printers are provided with a plurality of orifices, each orifice being associated with a resistor. At the appropriate time, current is passed through the particular resistor associated with an orifice from which it is desired to expel ink (the resistor being selected by a microprocessor in the printer). This process is known as firing. The pattern of particular orifices selected at any instant determine the configuration of the letter, number, symbol, etc. that is printed on the paper.
A problem with ink-jet printers is the evaporation of the carrier fluid; for aqueous-based systems, the carrier fluid is, of course, water. Upon evaporation of the carrier fluid, components in the ink precipitate out and form a hard plug in the orifice. The presence of the hard plug can prevent proper firing of the ink, so that the ink is either partially or totally blocked from reaching the paper.
On the other hand, it is desirable to prevent the evaporation of the various constituents of the ink, without adversely affecting the firing of the ink. Efforts to develop suitable ink compositions are continually in progress.